The Mother series, know as Earthbound outside of Japan, has been one of those series that Nintendo, for some odd reason, has never been to keen on localising for Western audiences. In fact, the only game available here in the West is the Super Nintendo 1994 title called Earthbound; the second game in the trilogy.
It all started to change when Nintendo revealed that the first title in the Mother series was being localised, for the first time ever, in the form of Earthbound Beginnings as a game for the Wii U Virtual Console; leading fans to believe Nintendo was finally going to be bringing the whole Mother trilogy to the West.
Although Nintendo has addressed Mother 3 in the past, nothing has really hinted at them actually wanting to localise the 2006 Gameboy Advance title, but some new information has made its way online that claims Nintendo was seriously considering it.
According to Imran Khan, Senior Editor at Game Informer, Nintendo was actively working on localising Mother 3 for Western audiences, but decided to cancel the project due to some controversial aspects — stating that "It was full steam ahead for a while but upon re-evaluation there were aspects of the game that weren't going to go without controversy."
Khan didn't quite specify what exactly was that Nintendo thought it was controversial about Mother 3, but it is likely that it has to do with some dry humour that may have not teanslated well outside of Japan; keeping in mind that the series does have some dark humour that isn't for everyone.
Mother 3 being localised for Western audiences is something that fans have been longing for since the game came out in April of 2006 in Japan, and it seems that they will still have to keep waiting for Nintendo to finally do something with the series as a whole. A "Mother Trilogy" remaster for the Nintendo Switch would be a great idea but, sadly, the ball is on Nintendo's side of the court.